1. Field of the Invention
The present invention relates generally to an apparatus and method for providing an enhanced uplink dedicated channel (EUDCH) service in an asynchronous CDMA (Code Division Multiple Access) mobile communication system, and in particular, to a scheduling apparatus and method for determining a noise rise over thermal noise (ROT) for each cell to provide an EUDCH service.
2. Description of the Related Art
The 2nd generation mobile communication systems focusing on voice service include GSM (Global System for Mobile Communications) and IS (Interim Standard)-95. GSM was deployed in 1992, mainly in Europe, and adopts TDMA (Time Division Multiple Access) for providing service. Alternatively, Korea and the United States adopted IS-95, which uses CDMA.
Currently, mobile communication technology has evolved to 3rd generation mobile communication systems for additionally providing data service and multimedia service at high rate with high quality. The 3rd generation mobile communication systems refer to a mobile communication scheme that supports packet service as well as voice service in CDMA. They include 3GPP (3rd Generation Project Partnership, or UMTS) based on asynchronous timing between Node Bs, and 3GPP2 (3rd Generation Project Partnership 2, or CDMA2000) based on synchronization between base stations.
The synchronous and asynchronous 3rd generation mobile communication systems are undergoing standardization for high-speed, high-quality wireless data packet service. As an example, the 3GPP is standardizing HSDPA (High Speed Downlink Access), and the 3GPP2 is developing standards for 1×EV-DV (Evolution-Data and Voice). The standardization work is a major example of efforts to explore a solution for providing a high-quality wireless data packet service at a high rate of 2 Mbps or above. The 3GPP further proposed EUDCH as a way of enabling high-speed packet transmission from a UE (User Equipment) to a Node B aside from high-speed packet transmission from the Node B to the UE. EUDCH attempts to improve the performance of packet transmission in the uplink communication of an asynchronous CDMA mobile communication system. The novel technology, EUDCH still uses AMC (Adaptive Modulation and Coding) and HARQ (Hybrid Automatic Retransmission Request), which were developed for HSDPA. However, a short frame having a shorter TTI (Transmission Time Interval) than TTI for HSDPA is used to transmit packets at high rate by fast reflecting uplink channel condition in EUDCH. That is, EUDCH and HSDPA differ in AMC and HARQ periods. TTI is defined as a transport unit for delivering one data block on a physical channel. For example, the TTI is 2 ms in EUDCH.
Accordingly, there is a need for scheduling uplink channels to assign resources to each cell appropriately, in addition to AMC, HARQ, and the short TTI. The uplink channel scheduling pursues efficient use of limited radio resources. For example, a target ROT (T_ROT) is determined for each cell through the uplink channel scheduling, to thereby maintain a measurement ROT (M_ROT) constant for the cell. That is, there may be a T_ROT as an optimal ROT to be maintained according to the states of a cell and its neighbor cells, and best system performance can be achieved when M_ROT as an actual ROT is prevented from exceeding T_ROT by uplink channel scheduling.
ROT is defined in Equation (1):
                    ROT        =                              I            o                                N            o                                              (        1        )            where Io is the sum of all received signal strengths in a Node B, namely, the overall wide-band received power spectral density of the Node B, and No is the thermal noise power spectral density of the Node B.
Because No is changed little for a predetermined time, ROT is dominantly dependent on Io. If ROT is small, this indicates that the strength of signals received in the Node B is weak. Although noise is small for UEs, the weak received signal limits the amount of traffic for the Node B. However, if the ROT is great, more traffic is delivered to the Node B. Unfortunately, the large ROT indicates an increased noise for the UEs. The resulting degradation of link performance leads to the degradation of the whole system performance. In view of the trade-off relationship between ROT and the whole system performance, an optimal ROT that maximizes the whole system performance must be achieved considering the traffic in the Node B and the noise strength at the UEs.